1. Field of the Invention
The present invention relates to a polarizing element, a method of manufacturing the polarizing element, a method of evaluating an exposure apparatus using the polarizing element, a method of manufacturing a semiconductor device, and the exposure apparatus.
2. Description of the Related Art
An exposure apparatus has been widely used to expose a circuit pattern of the liquid crystal display device or semiconductor device. The exposure apparatus can perform the so-called lithography process in which the original pattern formed on a photomask is reduced and transferred to the substrate. With requirements for smaller semiconductor devices, the shorter wavelength of the light source and the larger diameter of the projection optical system have been promoted for the higher resolution performance. An exposure apparatus with a NA of 0.9 or more using the ArF excimer laser of 193 nm wavelength is going from the development stage to the practical application stage. An ArF immersion-type exposure apparatus has been developed which fills liquid in a space between the lowest lens of the projection optical system and the substrate and can provide a NA of 1.0 or more on an air basis. A F2 exposure apparatus has also been developed which uses the F2 excimer laser of 157 nm wavelength. F2 immersion-type exposure apparatus has also been discussed.
In such a larger-diameter exposure apparatus, the polarization has become an important factor, which polarization was hardly seen as a problem in the conventional exposure apparatuses. The conventional exposure apparatuses have often converted the laser light from the light source device into non-polarized state before illuminating the mask. The non-polarized light includes an equal amount of an s-polarized component and a p-polarized component. The p-polarized component decreases the image contrast in the larger-diameter exposure apparatus. Before projecting the non-polarized light, therefore, the exposure apparatus needs to convert the non-polarized light into tangential linear polarization which includes more s-polarized component.
An optical element called a polarizing element has been used to control the polarization state. The polarizing element generally falls into a prism-type element and a filter-type element.
The prism-type polarizing element uses the nature of the birefringence or Brewster Angle or the like. The prism type is characterized by a smaller extinction degree (an extinction ratio for the arrangement in the crossed nicols condition) and a higher polarization performance. The prism-type element, however, suffers from problems in which it has a larger thickness and needs a larger installation space and has a small viewing angle.
In contrast, The filter-type polarizing element generally has poorer polarization characteristics than the prism-type element. The filter-type element has, however, advantages that it can be formed more thinly and be located in a smaller installation space and has a larger viewing angle (obliquely-incident light acceptable), or the like. By way of example, the filter-type polarizing element can be formed by rolling in one direction a glass substrate mixed with conductive particles such as the silver halide and forming the silver halide particles into a hyperelliptical shape. The hyperelliptical-shaped silver halide particles cause the anisotropic electric conduction which provides the polarization characteristics. The filter-type polarizing element cannot, however, apply to the filters used in the ultraviolet light region. This is because it is impossible to roll fluorite or fluorine-doped quartz glass or the like, which is highly transparent even for the ultraviolet light, with silver halide particles mixed therein.
Another well-known form of the filter-type polarizing element is a polarizing element called a wire grid polarizer (WGP). The wire grid polarizer (WGP) includes a glass substrate on which metal thin lines such as aluminum are equally spaced. The wire grid polarizer uses the anisotropic electric conduction as in the above-described polarization filter. The WGP needs to have the metal thin lines located in an interval sufficiently smaller than the wavelength of the light to be polarization-controlled. The WGP is currently in practical use only for the wavelength longer than the infrared region due to the restricted machining accuracy. It has been reported that at the laboratory level an electron beam lithography device can produce WGP of about 200 nm cycle, which WGP can even control the polarization of the visible light. The WGP has been partially commercially available (see U.S. Pat. No. 6,108,131).
It is not expected, however, that the WGP can provide the filter-type polarizing element that can control the polarization of the light in a deep-ultraviolet region (with a wavelength of 200 nm or less). To provide the filter-type polarizing element available in an exposure apparatus using an ArF excimer laser of 193 nm wavelength or a F2 exposure apparatus using a F2 excimer laser of 157 nm wavelength using the WGP, the metal thin lines need to be located in an interval of 50 nm or less. This is hard to realize with the current electron-beam machining technology.
Japanese application patent laid-open publication No. 2004-102217 or the like has suggested a polarizing element that is formed by closely arranging the carbon nanotubes on a transparent substrate, which carbon nanotubes have received attention as the new nano carbon materials. Japanese application patent laid-open publication No. 2004-102217 has disclosed a polarizing element that is formed by growing a plurality of carbon nanotubes, extracting a bundle of carbon nanotubes with tweezers or the like, and closely arranging the bundle on a transparent substrate. Note that, although not relating to the polarizing element, Japanese application patent laid-open publication No. 2003-257304 and Y. Chan et. al., Appl. Phys. Lett. 76, 2469 (2000) are well known to disclose the method of arranging the carbon nanotubes.
However, the method disclosed in the patent laid-open publication No. 2004-102217 has the difficulty in extracting long carbon nanotubes ropes because the strength of adhesion between adjacent nanotubes is not uniform, so long aligned ropes of nanotubes cannot be obtained by that method.
Furthermore, the above-described Japanese application patent laid-open publication No. 2004-102217 discloses a polarizing element that uses a silicon substrate, which cannot transmit light with a shorter wavelength than the visible light. In addition, the patent performs heat treatments of 400 degrees Celsius/10 hrs and 650 degrees Celsius/5-30 min, which may cause color centers in the quartz substrate used in the present invention. The patent thus cannot provide a polarizing element available in the deep-ultraviolet region (with a wavelength of 200 nm or less).